Google has revealed that it ignores the “keywords” meta tag in its web search ranking. Google’s Matt Cutts explains this in a Webmaster Central video
“About a decade ago, search engines judged pages only on the content of web pages, not any so-called “off-page” factors such as the links pointing to a web page,” says Matt. “In those days, keyword meta tags quickly became an area where someone could stuff often-irrelevant keywords without typical visitors ever seeing those keywords. Because the keywords meta tag was so often abused, many years ago Google began disregarding the keywords meta tag.”
This does not mean that Google ignores all meta tags, the title tag is still a very powerful and critical search ranking factor, the “description” meta tag is often used to display the snippet of you web page in the search results, while this does not influence ranking it could be a used effectively to convert clicks by using appropriate call to action elements in your “description” meta tag.
Google also recognizes the “google,” “robots,” “verify-v1,” “content type,” and “refresh” meta tags. Information about how Google understands these can be found in the Google Webmaster Tools help center.
Matt Cutts referring to “keywords” meta tag says, “It’s possible that Google could use this information in the future, but it’s unlikely, Google has ignored the keywords meta tag for years and currently we see no need to change that policy.”
However it is possible that other search engines might use the information to influence search ranking but Google doesn’t.